Refused to settle back to sleep in middle of night?

Hi

Hoping someone can shed some light on last nights events. My LO (who is turn about to turn 9 months old) has only recently starting sleeping through the night (from 7 to 7). He's not doing it every night yet but most. However last night (and one night last week also) he woke at about 4am and just refused to settle back to sleep after being fed. He took feed okay and was quite happy to go all quiet in my arms but just wouldn't settle back to sleep afterwards. Eventually got him to sleep but after best part of two hours since he woke! He didn't appear to be still hungry as he had taken himself off breast and wasn't interested in going back on. Wasn't upset when in my arms but would start (and stay) crying as soon as he was put back down in his cot. I tried cuddling/rocking but would wake as soon as I put him down, tried leaving him cry (lot of time was more a whinge rather than cry) but didn't work. Didn't change his nappy as didn't want to wake him further but nappies never seem to bother him.

Previously when he used to wake for night feed he would have it and go straight back to sleep. This may be a once (or twice) off but has anyone any thoughts on what might have caused it? Would like to try to nip in the bud before it becomes habit forming.

Thanks in advance

could he be teething hun? DD2 is a bit like that at the moment but shes just screaming! not so much fun.
or it could just be a phase he's going through

Sorry should have included about teething. Doubt very much its teething as his 4th tooth has just come through a few days ago and can't even see or feel the next lot so had kindof discounted that one. He's not unhappy when he is up only when I put him back into his cot!